Keep the battery warm if you want to fast charge in the winter

One of the Chevrolet Bolt EV users - Ste - tested the fast charging capabilities of the car at 28°F (-2°C) and shared thoughts on how to not waste time and money at the DC fast chargers.

The bottom line is that the lithium-ion batteries' charging power (which translates to speed) is limited by temperature. From around 0°C typically there is a significant slowdown - the colder the battery is, the slower it will charge. The slowdown can be higher than an order of magnitude - for example, you might take on just a few kW instead 50-100 kW - at least until the battery warms up.

In the case of Ste's Chevrolet Bolt EV, the deeply discharged and cold battery was able to accept less than 15 kW from a 50 kW EVgo charger, which triples the time and expense (if charging fee is by minutes).

The charging hardly exceed 15 kW after 10 minutes, and then slowly increased to 20 kW after 25 minutes. The last 15-20 minutes brought charging to over 30 kW as the battery has warmed to levels that permit a faster charge rate.

After some 45 minutes of charging, only 17.1 kWh was dispensed.

"As winter arrives and freezing temperatures settle in on large parts of North America, it's important to understand that a cold battery significantly impacts range and charge rate.

The latter might not be as familiar to new electric vehicle owners, which is why I ran through this example winter charging session on my Chevy Bolt EV to show what you can expect.

Time Stamps:

1:08 - Location 1:30 - Three EVs / Two EV spaces 2:12 - Start of Charge / Lame Rate 9:50 - The Slow Crawl to Medium Speed 12:52 - Finally Getting Warm 14:15 - 45 Minute Auto-shutoff + Review 16:14 - Finishing Up + Planning Moan

Other models may fare better, but the key takeaway is to do what you can to keep your battery warm in winter, or at least warm it up before you waste time and money on elongated DCFC sessions. My intention is to also test whether a short period on a (free/cheaper) level 2 charger before hitting the more expensive DCFC would help expedite the battery warming process, but that will have to wait for another session when we have similar temperatures.

Also a sidebar to electric vehicle charging planners: try to include at least as many EV-only spaces as you have charging units!"

In the second test (see video below), when the battery was warmed up after driving, 17.4 kWh was dispensed in just 23 minutes, which is twice as fast and could be half as cheap.

The side effect of charging with a warm battery is it's quicker, so the station can serve more customers.

"Following a frankly painful first winter charging test session with a cold Bolt EV battery, here's our second attempt at similar ambient temperatures but with the vehicle battery warmed up after driving.

The results are immediate and obvious, but still provide food for thought to new EV owners. Time Stamps:

1:20 - Pulling in (Ghost Mall) 1:47 - Pre-charge recap 2:10 - Starting a charge session on EVgo 3:10 - Charge starts up 4:20 - Charge in progress/Dash close-up 6:40 - 10 minutes elapsed + session comparison 7:26 - Discussing EVgo rates + why you need a plan 8:55 - Discussing how to price out a charge session 11:28 - 20 minutes elapsed + session forecast 13:48 - Target reached + charge stopped: Summary 14:30 - Heading out + pondering Electrify America installations next to existing EVgo mall locations

If this is your first winter with a Chevrolet Bolt EV or any other electric vehicle, do what you can to warm the battery before attempting a fast charge session. That typically means driving at highway speeds for an prolonged period of time, but I'll be researching/testing other potential approaches in the weeks ahead... the more you know!"

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